fix(evidence): enforce active vector generations

harness/tht/adapters/vector/thoth_http.py

@@ -40,7 +40,8 @@ class ThothHttpVectorStore:
     def capabilities(self) -> VectorCapabilities:
         writable = self._writer is not None
         return VectorCapabilities(
-            search=self._reader is not None, existing_hashes=writable, upsert=writable
+            search=self._reader is not None, existing_hashes=writable, upsert=writable,
+            metadata_filter=self._reader is not None, delete_generation=writable,
         )
 
     def health(self) -> VectorHealth:
@@ -91,6 +92,7 @@ class ThothHttpVectorStore:
         *,
         limit: int,
         kinds: list[str] | None = None,
+        metadata_filter: dict[str, object] | None = None,
     ) -> list[VectorHit]:
         require_positive_limit(limit)
         if self._reader is None:
@@ -103,7 +105,13 @@ class ThothHttpVectorStore:
         for collection in collections:
             _collection("vectors", collection)
             try:
-                rows = self._reader.search_similar(collection, embedding, limit, kinds=kinds)
+                if metadata_filter is None:
+                    rows = self._reader.search_similar(collection, embedding, limit, kinds=kinds)
+                else:
+                    rows = self._reader.search_similar(
+                        collection, embedding, limit, kinds=kinds,
+                        metadata_filter=metadata_filter,
+                    )
             except VectorRestError as exc:
                 raise VectorStoreError(str(exc)) from exc
             hits.extend(
@@ -144,6 +152,14 @@ class ThothHttpVectorStore:
         except VectorRestError as exc:
             raise VectorStoreError(str(exc)) from exc
 
+    def delete_generation(self, collection: str, generation: str) -> int:
+        if collection != "evidence" or not generation.startswith("gen:"):
+            raise VectorStoreError("Only exact Evidence generations may be deleted")
+        try:
+            return self._require_writer().delete_generation(collection, generation)
+        except VectorRestError as exc:
+            raise VectorStoreError(str(exc)) from exc
+
     @staticmethod
     def _row(write_record: VectorWriteRecord) -> dict:
         record = write_record.record